Annealing titanium wire



y 3, 1968 w. M. PARRIS I ANNEALING TITANIUM WIRE Filed July 26, 1965INVENTOR Warren M. Porris United States Patent 3,394,036 ANNEALENGTITANIUM WIRE Warren M. Parris, Las Vegas, Nev., assignor to TitaniumMetals Corporation of America, New York, N.Y., a corporation of DelawareFiled July 26, 1965, Ser. No. 474,764 3 Claims. (Cl. 148-11.5)

ABSTRACT OF THE DISCLOSURE Method of reducing the cross section oftitanium and titanium base alloy wire which has been previously hotrolled at a temperature below its beta transes comprising heating thewire to a temperature between the beta transes and about 100 F. abovethe beta transes followed by cooling to below the beta transes and colddrawing.

This invention relates to heat-treating wire and more particularly toannealing titanium or titanium base alloy wire to provide improvedcold-rolling characteristics.

Conventional wire processing involves first hot-rolling to form arelatively large diameter wire which is subsequently cold drawn, oftenwith several passes, through a die to provide the desired finisheddiameter. Instead of drawing through a die, the wire may be cold workedto finished diameter by passing through multiple circumferential rollershaving grooved edges. Adjacent edges of the working rollers form acircular aperture so that the wire is worked down to provide the desiredfinished diameter by a rolling instead of a simple drawing operation.

A serious problem arises in production of such cold formed titanium andtitanium alloy wire. Initial hot-rolling, most often accomplished at atemperature below the beta transes temperature and in the alpha-beta oralpha temperature field, produces a definite texture or preferredcrystal orientation in the hot-rolled wire. When wire of this type oftexture or orientation is subsequently coldrolled through a multipleroller finishing machine, the resistance of the wire to deformation isnot uniform and the cross section of the cold-rolled wire will not beuniform and may actually be oval.

Summarized briefly, the process of this invention comprisesheat-treating titanium and titanium alloy wire at a temperature aboveits beta transes to eliminate the crystal orientation imparted byprevious hot-rolling at a temperature below its beta transes. Thisparticular heating step, I have discovered, particularly in the case oftitanium alloys, must be carried out so that the wire is heated rapidlyto the heat-treating temperature, and then preferably cooled rapidly toprevent the, formation of large-size beta grain structure. When the wireis heattreated in this manner, being quickly raised to temperature andthen quickly cooled, it can be reduced to final gauge through a rollertype wire drawing machine to produce wire of circularity substantiallyimproved over similar wire drawn without such heat-treatment, Inaddition, the ductility of the wire will be high so that its crosssectional area may be reduced by a substantial percentage in a singlepass through the roller wheels without cracking or breaking of the wire.

The process of this invention may be more readily understood byreference to the single figure of the drawings in which a drum or coilof wire, which has previously been hot-rolled at a temperature below itsbeta transes, is shown at 2. The wire 4 is directed into resistanceheating furnace 6 in which are arranged two sets of contact rollersindicated at 8 and 10 respectively, these two sets of rollers beingspaced apart along the wire and each connected to a pole of a suitablesource of electric current 12. The section of wire 4 between contactrollers 8 and 10 will complete the electrical circuit, and because ofits own internal resistance, will be very rapidly raised to hightemperature. Immediately on emergence from furnace 6 the wire is exposedto a blast of cooling air 14 provided by blower 16.

After cooling, the wire is pulled through a set of edgegrooved rolls 18,these in the illustration being a set of three arranged around the wireat a radial angle of each to the other with their edge grooves 20forming a circular aperture through which the wire 4 is pulled by actionof bull block 22 actuated by a suitable motor (not shown).

For simplicity and clarity and to illustrate the essential steps of theprocess, only one set of rolls 18 have been shown in the drawing. Inpractice, at least a pair of such sets, preferably nested to provideclose coupling, will generally be employed so that the wire may bereduced in diameter in a plurality of steps. The first set of a pair mayadvantageously reduce the wire and give it a curved-side triangle crosssection or oval or other non-circular shape, with the second and finalset of rolls providing a circular aperture to impart the desiredcircular cross section.

The wire whose cross section is to be reduced by th method of thisinvention is characterized by having been previously worked at atemperature below its beta transes. It is common practice in wiremanufacture to work commercially pure and alpha and alpha-beta typetitanium base alloys in the alpha-beta field or alpha field because thisprovides easiest plastic deformation without raising the temperature ofthe material to a point where rapid oxidation and surface deteriorationtakes place. Moreover, working in the beta field will generally resultin larger grains which are difiicult to break down in subsequent workingat lower temperatures. The process of this invention is to be applied towire whose latest prior working will have been hot-rolling at atemperature below its beta transes because this type of rollingapparently produces a detrimental crystal structure which affectssubsequent cold-rolling when the wire is drawn through edge-groovedrolls. Apparently hot-rolling at such temperatures results in anorientation of the metal crystals so that subsequent deformation willnot be uniform in all directions. Particularly when the hot-rolled Wireis drawn through edge-grooved rolls the ease of deformation in a planeperpendicular to the length of the wire will not be uniform at variousradial angles in this plane. Consequently, such wire when cold drawnthrough edgegrooved rolls will deform more readily in certain areas ordirections, and this will often result in an oval wire instead of havingdesired circular cross section. It appears that the edge-grooved rolls,no matter how strongly built and precisely aligned to produce a circularorifice through which the wire is drawn, can be deformed elastically tosome extent so that wire having preferred crystal orientation, whenpassing through such rolls, will not produce a truly circular or uniformreduced cross section wire.

According to this invention, however, heating the wire to above its betatranses and subsequently cooling the wire with attention to rapidheating and cooling, for the titanium base alloys particularly, results:in an annealed wire of uniform crystal orientation which, when colddrawn through edge-grooved rolls, can be reduced to produce a circular'wire of substantially uniform diameter.

The wire should be heated to a temperature definitely above its betatranses temperature, which may be determined for commercially puretitanium or any of the alpha or alpha-beta type titanium base alloys bymetallurgical methods well known in the art. The minimum time that thewire is maintained above its beta transes temperature is not critical,since apparently transformation takes place almost instantaneously; andonce the wire has been raised to above its beta transes and subsequentlycooled, the time above the beta transes temperature, even though but afew seconds, will be sufiicient to produce the desired transformation ofthe crystal structure. It is preferred to heat the wire to a temperaturebetween its beta transes and 100 F. above its beta transes in order tobe sure that all portions of the wire have definitely been raised toabove the beta transes temperature. Preferably the heat treatingtemperature is between the beta transes temperature and about 50 F.above the beta transes. While the temperature should be sufficientlyhigher than the beta transes to insure complete transformation, it isnot desirable to raise to excessive temperature since this inevitablyresults in increased time above the beta transes, and also results in atendency towards formation of large beta grains.

The time for the heat-treating step of this invention is extremelycritical, and for alpha and alpha-beta type titanium base alloys thetotal elapsed time for heating the wire from room temperature to aboveits beta transes plus the time it is maintained above its beta transesshould not be greater than one minute. Preferably for best results withwire of the recited titanium base alloys the time should not be morethan 30 seconds. For comcient that the temperature be rapidly reduced,and to accomplish this, air cooling will produce a relatively fast andefficient reduction of wire temperature from its annealed temperaturedown to room temperature and particularly at least through the betatranses temperature.

After heat-treatment and subsequent cooling, the wire is cold drawnthrough a set of edge-grooved rolls to produce circular wire ofsubstantially uniform diameter. Table 1, following, provides examples ofheat-treating commercially pure titanium wire above its beta transestemperature and subsequently cold drawing this through two sets ofnested edge grooved rolls to produce wire of improved circularity. Thewire was of commercially pure, unalloyed titanium designated in thetrade as Ti-SSA. The original ingot of the commercially pure titaniumwas worked down through various stages, the wire being rolled on a hotmill starting at a temperature of about ]750 F. and finishing at atemperature of about 1300 F. The latest prior working (at 1300 F.) wasin the alpha field. Table 1 shows the heat-treatment prior to drawingthrough the edge-grooved rolls, the starting diameter of the wire, whichwas measured as maximum and minimum diameters along a 10-foot length ofwire, and also the diameter measured in the same manner after colddrawing through the edgegrooved rolls.

TABLE 1 Variation in Starting Variation in DiameterAfter Diameter ofHeat-Treatment Prior to Drawing Diameter Starting Drawing 1 Cold Drawn(inch) Diameter (inch) (inch) Wire (inch) As Mill Annealed 266-. 277 0.011 .246-. 251 0. 005 1,300 F. (2 Hrs.) AC 2 71-. 280 0. 009 .246. 2570, 011 Heat-Treated Above Beta Transes:

1,750 F. (10 See.) A 1641274 0.010 .2465.248 0.0015 750 F. (10 Sec AC 2267-. 276 0. 000 2465-. 248 0.0015 1,750 F (15 Min.) AC 2 258-. 271 0.013 246-. 247 0. 001 1,750 F. Min. AC .259. 272 0. 013 .246. 248 0.0021,750" F (1 B AC 265-. 275 0.010 .246. 248 0.002

1 Maximum and minimum diameters along 10-fo 0t length of wire. 2 Totaltime heating to temperature and air cooling.

mercially pure titanium, the time is not so critical. I have found someimprovement with shorter times, but wire of commercially pure titaniummay be heat-treated through a cycle from room temperature to above thebeta transes plus the time at or above the beta transes, which takes nomore than one hour.

The short time requirements for the heat-treating step of this inventionrequires means for heating wire very rapidly to high temperature. Thiscan readily be accomplished by resistance heating or induction heating.In resistance heating, heavy electrical currents are passed through alimited section of the wire, and the current flow results in extremelyrapid heating of the wire. It is no problem to raise the wiretemperature to above its beta transes temperature in a matter of secondswhen passing a sufficient amount of current. In induction heating, thewire is subjected to high frequency induced electric current, and thisalso will raise the temperature of the wire extremely rapidly; andraising to above the beta transes by induction heating can beaccomplished well within the time limits hereinbefore recited. Whenheattreating commercially pure titanium wire, and for which the time isnot so critical, coils of wire may be furnace heat-treated, which takesappreciably longer than the other two methods suggested, but totalheat-treating time may still be maintained within a desirable periodunder an hour.

Once the heat-treated wire has been raised to above its beta transestemperature, it is then quickly cooled, at least down through its betatranses. This may be accomplished by any convenient means providing arelatively rapid cooling. Quenching, which involves submerging the hotwire in water or oil and results in an almost instantaneous cooling, canbe employed, if desired, although such a fast cooling effect is notessential to satisfactory results according to this invention. It issufii- It will be seen from Table 1 that with a heat-treatment below thebeta transes with subsequent rapid cooling, the variation in wirediameter will be improved from about 0.011 inch to 0.005 inch in themill annealed condition when heated at 1300 F. When heat-treatment abovethe beta transes is employed, however, the variation in wire diameter isreduced from a starting figure of between 0.013 inch and 0.009 inch downto a maximum of 0.002 inch, and under the most rapid heating and coolingconditions, less even than this. The beta transes of the Ti-SSAcommercially pure titanium metal was 1675 F. so that the betaheat-treatments used were all about above the beta transes temperatureof the alloy. It will be seen from the variation in diameter of the colddrawn wire that the tests run using longer heating and cooling periods,that is 30 minutes to 1 hour, showed less favorable variation in wirediameter than the tests run at shorter periods of time.

Table 2, following, provides examples of heat-treating alpha-beta typetitanium base alloy above its beta transes temperature and subsequentlycold drawing this through multiple edge-grooved rolls to produce wire ofimproved circularity. The wire was of an alloy comprising 8% aluminum,1% molybdenum, 1% vanadium, and balance substantially all titanium. Theoriginal ingot of titanium base alloy was worked down through variousstages, the wire being rolled on a hot mill starting at a temperature ofabout 1950 F. and finishing at a temperature of about 1400 F. to 1500 F.The latest prior working (at 1400 F. to 1500 F.) was in the alpha-betafield. Table 2 shows the heat-treatment prior to drawing through theedgegrooved rolls, the starting diameter of the wire, which was measuredas maximum and minimum diameters along a 4-foot length of wire, and alsothe diameter measured in the same manner after drawing through theedgegrooved rolls. The variations in starting diameters and in thediameters after drawing through the edge-grooved rolls as well as thereduction in area and observations with respect to cracking duringdrawing are also shown in the table.

TABLE 2.-8Al-1Mo-1V ALLOY Starting Variation in Diameter Variation inReduction Diameter Starting After Draw- Diameter of in Area, Remarks(inch) Diameter, ing (inch) Cold Drawn Percent (inch) Wire, (inch)Heat-Treatment Prior to Drawing: 276-. 279 0. 003 243-. 249 0.006 21. 5Severe Cracking.

1,850 F. (5 min.) AC 2 (cts Anneal). .279-. 282 0. 004 .254. 260 0. s15. OK, No Cracks.

. 276-. 280 0. 004 252-. 256 0. 004 16. 5 Do. 276-. 278 0. 002 252-. 2560. 004 16. 0 Do.

Average 0. 0035 0. 005

Heat-Treated Above Beta Transes: 280-. 285 0. 005 245-. 247 0. 002 24Do. 1,950 F. (10 Sec.) AC. 2 279-. 283 0. 004 245-. 246 0 001 24 D0.281-. 283 0. 002 245-. 247 0 002 24 Do. 279-. 283 0. 004 244-. 246 0.002 24 Do.

Average 0. 004 0. 002

1 Maximum and minimum diameters along 4-foot length of wire. 2 Totaltime heating to temperature and air cooling.

It will be seen from Table 2 that with a heat-treatment below the betatranses and followed by subsequent rapid cooling, the variation in wirediameter will not be improved in the case of the 8Al-1Mo-1V alloy. Thetest results indicate that after a heat-treatment at 185 0 F. thevariation in starting diameter averaged 0.0035 inch; and this was madeworse by cold drawing, the average after this step being 0.005 inch. Itwill also be seen from the results shown in the upper portion of Table 2that cold drawing to produce a reduction in area of as much as 21.5%resulted in severe cracking of the product wire, although reductions inthe range of 15.5% to 16.5% could be obtained with no cracks. When the8Al-1Mo-1V wire was heat-treated at a temperature above its betatranses, that is at 1950 F. (its beta transes being 1900 F.), and

The original ingot of the titanium base alloy was worked down throughvarious stages, the wire being rolled on a hot mill starting at atemperature of about 1850 F. and finishing at a temperature of about1300 F. to 1400 F. The latest prior working (at 1300" F. to 1400 F.) wasin the alpha field. Table 3 shows the heat-treatment prior to drawingthrough the edge-grooved rolls, the starting diameter of the wire, whichwas measured as maximum and minimum diameters along a 4-foot length ofwire, and also the diameter measured in the same manner after drawingthrough the edge-grooved rolls. The variations in starting diameters andin the diameters after drawing through the edge-grooved rolls as well asthe reduction in area, and observations with respect to cracking duringdrawing, are also shown in the table.

TABLE 3.5A1-2.5S11 ALLOY Starting Variation in Diameter Variation inReduction Diameter, 1 Starting After Draw- Diameter of in Area, Remarks(inch) Diameter, ing, 1 (inch) Cold Drawn Percent (inch) Wire (inch)Heat-Treatment Prior to Drawing: 287-. 305 0.018 261-. 268 0. 007 20Severe Cracking. 1,850 F. (5 Min.) AC 2 (a-fi Anneal). 287-. 306 0.019267-. 273 0.006 16. 5 OK, No Cracks.

. 288-. 308 0. 020 264-. 273 0. 009 19 Do. 290-. 306 0. 016 264-. 273 0.009 19 Do. 286-. 306 0. 020 264-. 271 0. 007 18 D0. 3 264-. 271 0. 007 3242-. 247 0. 005 32 Severe Cracking.

Average 0. 016 0. 007

Heat-Treated Above Beta Transes: .293-. 311 0. 018 261-. 264 0.003 24. 5OK, No Cracks.

1,950 F. (10 Sec.) AC 2 291-. 307 0. 016 262-. 264 0. 002 22. 5 Do.289-. 303 0. 014 260-. 263 0.003 22. 0 Do. 290-. 306 0. 016 260. 263 0.003 22. 0 D0.

Average 0. 016 0.003

a .261-. 264 0. 003 3 244-. 24s 0. 002 n 34 Do. 5 260-. 263 0.003 3244-. 246 0. 002 34 D0. 3 260-. 263 0. 003 3 244-. 246 0. 002 34 Do. 3.262-. 264 0. 002 3 .244. 246 0. 002 34 Do.

Average 0. 003 0. 002

1 Maximum and minimum diameters along 4-foot length of wire.

2 Total time heating to temperature and air cooling.

3 Second reduction without intermediate anneal.

rapidly cooled by air cooling, the variation in diameter before andafter drawing through the edge-grooved rolls was reduced from an averageof 0.004 inch to an average of 0.002 inch. Thus it is seen that thecritical heat-treating and rapid cooling resulted in a substantialimproved circularity and uniformity of diameter of the cold drawn wire.Additionally, it will be noted that after heat-treating according tothis invention and cold drawing through the edge-grooved rolls, areduction in area of 24% could be readily obtained without cracking ofthe wire product, and this compares with substantially less reductionobtainable without the specific he-at-treatment employed according tothis invention and shown in the upper part of the table.

Table 3, following, provides examples of heat-treating an alpha typetitanium base alloy above its beta transes It will be seen from Table 3that with a heat-treatment below the beta transes with subsequent rapidcooling, the variation in wire diameter was improved in the case of the5Al-2.5Sn titanium base alloy only from an average of 0.016 inch to anaverage of 0.007 inch. In addition, it will be seen that severe crackingoccurred when sufiicient working was employed to provide a reduction inarea during cold drawings through the edge-grooved rolls of 20%. Whenthe reduction was reduced below 20%, cracking was avoided. The lastresult in the group of tests in which the alloy wire was heat-treated at1850 F. prior to cold drawing through the edge-grooved rolls was given asecond reduction without intermediate anneal so that the total reductionamounted to 32%. Apparently the alloy wire was not sufficiently ductileto maintain its integrity 7 under this degree of reduction and severecracking resulted.

In the group of tests which were heat-treated above the beta transes ofthe alloy, namely at 1950 F. and then rapidly reduced in temperature byair cooling, the average variation in starting diameter was reduced from0.016 inch down to 0.003 inch. The beta transes of the Al-2.5Sn alloy is1900 F. In the upper group of tests in which the wire had beenheat-treated above its beta transes, it will be seen that reduction inarea of as high as 24.5% could be obtained without any deleteriouseffect on the wire, that is without formation of cracks. In the lowergroup of tests in Table 3, also heat-treated at 1950 F. and rapidlyreduced in temperature by air cooling, the wire was given a secondreduction without intermediate anneal to provide a total reduction inarea of 34%. The variation in starting diameter was reduced under theseconditions into stages, that is from an original 0.016 inch down to0.003 inch and then from 0.003 inch down to 0.002. inch in the secondreduction. While the improvement in variation of diameter in the colddrawn wire in the second reduction stage is insignificant and alsoimmaterial (since the starting diameter variation was already extremelylow) a significant effect is seen in the amount of reduction which canbe obtained without cracking in the product wire. It is shown under thetest conditions that the wire can be reduced a total of 34% and stillproduce good wire without cracks. In the case of wire not heat-treatedabove its beta transes and shown as the bottom test of the upper groupin Table 3, a combined reduction of 32% resulted in severe cracking inthe wire product.

I claim:

1. A method for reducing the cross section of wire of metal selectedfrom the group consisting of commercially 35 pure titanium andalpha-type and alpha-beta-type titanium base alloys, the latest priorworking of said wire being hot-rolling below its beta transestemperature, which comprises:

(a) heating said wire to a temperature between its beta transestemperature and about 50 F. above its beta transes temperature andsubsequently cooling said wire to below its beta transes temperature,the total elapsed time for heating said wire from room temperature toabove its beta transes temperature plus the time it is maintained aboveits beta transes temperature being not greater than one minute; and,

5 (b) cold drawing said wire through edge-grooved rolls, whose edgegrooves in adjacent alignment form a circular aperture to provide acircular wire of substantially uniform diameter.

2. A method for reducing the cross section of wire of metal selectedfrom the group consisting of commercially pure titanium and alpha-typeand alpha-beta-type titanium base alloys, the latest prior working ofsaid wire being hot-rolling below its beta transes temperature, whichcomprises:

(a) heating said wire to a temperature between its beta transestemperature and about 100 F. above its beta transes temperature andsubsequently cooling said wire to below its beta transes temperature,the total elapsed time for heating said wire from room temperature toabove its beta transes temperature plus the time it is maintained aboveits beta transes temperature being not greater than one minute; and,

(b) cold drawing said wire through edge-grooved rolls whose edge groovesin adjacent alignment form a circular aperture to provide a circularwire of substantially uniform diameter.

3. A method as set forth in claim 2 including passing electric currentthrough said wire after said hot-rolling whereby said heating isaccomplished by the resistance of 30 said wire to the passage of saidelectric current.

References Cited UNITED STATES PATENTS 2,804,409 8/1957 Kessler et al.1481l.5 3,169,085 2/1965 Newman 1481l.5

FOREIGN PATENTS 949,861 2/1964 Great Britain.

HYLAND BIZOT, Primary Examiner.

W. W. STALLARD, Assistant Examiner.

